It is known that carbon dioxide may be sequestered by mineral carbonation. In nature, stable carbonate minerals and silica are formed by a reaction of carbon dioxide with natural silicate minerals:(Mg,Ca)xSiyOx+2y+xCO2→x(Mg,Ca)CO3+ySiO2 The reaction in nature, however, proceeds at very low reaction rates. The feasibility of such a reaction in process plants has been studied. These studies mainly aim at increasing the reaction rate.
At the internet site of the US department of energy, http://www.fetc.doe.gov/publications/factsheets/program/prog006.pdf, for example, is disclosed the reaction of finely ground serpentine (Mg3Si2O5(OH)4) or olivine (Mg2SiO4) in a solution of supercritical carbon dioxide and water to form magnesium carbonate.
In WO02/085788 is disclosed a process for mineral carbonation wherein particles of silicates selected from the group of ortho-, di-, ring, and chain silicates, are dispersed in an aqueous electrolyte solution and reacted with carbon dioxide.
An alternative for the use of natural minerals as starting material for carbon dioxide sequestration is the use of industrial waste materials that contain calcium-comprising mixed oxides such as calcium silicate or calcium iron oxide. Mineral carbonation of industrial waste materials such as steel slag has been proposed. In ‘Accelerated carbonation of waste calcium silicate materials’ by D. C. Johnson (ISSN 1353-114X), for example, it is disclosed that stainless steel slag, deinking ash, pulverised fuel ash are suitable feedstocks for a carbon dioxide sequestration process.
The use of steel slag for mineral carbonation would, however, be more attractive if valuable product streams could be recovered from the carbonation process.